Project leader Thomas Quinn says the team will wait for results from ongoing trials in Kenya and Uganda before saying conclusively whether male circumcision limits HIV transmission from women to men only, or, as the new data suggest, from men to women also.

He says this could lead them to recommend that all men be circumcised.

Male circumcision is common in North America and among Jews and Muslims, but not generally in eastern and southern Africa, Europe or Asia.

The research is part of a larger study of 12,000 people in Uganda's Rakai district who are being monitored to determine how HIV spreads.

It has also found that early deaths from AIDS can be predicted by identifying the type of HIV virus infecting a patient.

"Knowing a patient's HIV type is important for managing the infection, because the disease can progress more quickly in some types than others," says Oliver Laeyendecker, who led this part of the study.

The team found that patients infected with HIV type D died more quickly than those infected with type A. Ten per cent of patients with HIV type D died within three years, while none of those infected with type A died during the same period.

The scientists think that type D kills more quickly than type A because it binds to key areas on immune cells.